Boiler and operating method of same

Abstract

A boiler operating method operates a boiler by switching between air combustion mode and oxygen combustion mode when burning fossil fuel with first combustion gas and second combustion gas. The second combustion gas compensates for oxygen deficiency in the first combustion gas. The air combustion mode uses air as the first combustion gas and the second combustion gas while the oxygen combustion mode uses mixed gas of combustion flue gas and oxygen-rich gas as the first combustion gas and the second combustion gas, the combustion flue gas being produced when the fossil fuel is burned. By mixing the oxygen-rich gas in the air in the process of switching between air combustion mode and oxygen combustion mode, the air being the first combustion gas used in the air combustion mode, the boiler operating method can switch between the air combustion mode and oxygen combustion mode while maintaining stable combustion.

The invention claimed is: 
     
       1. A boiler operating method comprising:
 burning a fossil fuel with a first combustion gas used to transport the fossil fuel and a second combustion gas used to compensate for oxygen deficiency of the first combustion gas; 
 switching operations between air combustion mode in which air is used as the first and the second combustion gas, and oxygen combustion mode in which mixed gas of combustion flue gas of the fossil fuel and oxygen-rich gas is used as the first and the second combustion gas; 
 in the process of switching from the air combustion mode to the oxygen combustion mode, mixing the oxygen-rich gas in the air used as the first combustion gas in the air combustion mode; and 
 switching the air to the mixed gas of the combustion flue gas and the oxygen-rich gas, wherein in the process of switching from the air combustion mode to the oxygen combustion mode, the oxygen-rich gas is mixed in the air used as the first combustion gas, and then the oxygen-rich gas is mixed in the second combustion gas. 
 
     
     
       2. The boiler operating method according to  claim 1 , further comprising:
 using the first combustion gas as carrier gas for transporting the fossil fuel, and 
 supplying part or all of the second combustion gas to a burner, wherein 
 the process of switching from the air combustion mode to the oxygen combustion mode undergoes (1) to (4) below in sequence: 
 (1) mixing the oxygen-rich gas in the carrier gas in the air combustion mode, and setting oxygen concentration in the carrier gas higher than oxygen concentration in the air; 
 (2) introducing the combustion flue gas of the fossil fuel into the first and second combustion gases; 
 (3) mixing the oxygen-rich gas in the second combustion gas; and 
 (4) stopping supplying the air to the first and second combustion gases. 
 
     
     
       3. The boiler operating method according to  claim 1 , wherein
 when the fossil fuel is burned with the mixed gas, the oxygen concentration in the first combustion gas is set lower than the oxygen concentration in the second combustion gas. 
 
     
     
       4. A boiler operating method comprising:
 burning a fossil fuel with a first combustion gas used to transport the fossil fuel and a second combustion gas used to compensate for oxygen deficiency of the first combustion gas; 
 switching operations between air combustion mode in which air is used as the first and the second combustion gas, and oxygen combustion mode in which mixed gas of combustion flue gas of the fossil fuel and oxygen-rich gas is used as the first and the second combustion gas; 
 in the process of switching from the air combustion mode to the oxygen combustion mode, mixing the oxygen-rich gas in the air used as the first combustion gas in the air combustion mode; and 
 switching the air to the mixed gas of the combustion flue gas and the oxygen-rich gas, wherein in the process of switching from the oxygen combustion mode to the air combustion mode, the mixed gas used as the second combustion gas is switched to the air, and then supply of the oxygen-rich gas mixed in the air used as the first combustion gas is stopped. 
 
     
     
       5. The boiler operating method according to  claim 4 , further comprising:
 using the first combustion gas as carrier gas for transporting the fossil fuel, and 
 supplying part or all of the second combustion gas to a burner, wherein 
 the process of switching from the oxygen combustion mode to the air combustion mode undergoes (1) to (4) below in sequence: 
 (1) supplying the air to the first and second combustion gases; 
 (2) stopping mixing the oxygen-rich gas in the second combustion gas; 
 (3) stopping introducing the combustion flue gas of the fossil fuel into the first and second combustion gases, and setting oxygen concentration in the carrier gas higher than oxygen concentration in the air and oxygen concentration in the second combustion gas; and 
 (4) stopping mixing the oxygen-rich gas in the carrier gas.